linux-kernel - Re: [PATCH v2 1/1] percpu-refcount: do not forget to rcu

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Message-ID: <20160810220932.GA2695@mtj.duckdns.org>
Date:	Wed, 10 Aug 2016 18:09:32 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Roman Pen <roman.penyaev@...fitbricks.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/1] percpu-refcount: do not forget to rcu_barrier()
 just before freeing

On Wed, Aug 10, 2016 at 09:55:39PM +0200, Roman Pen wrote:
> percpu issues some RCU callbacks to synchronize its state, so before
> freeing we have to wait all those callbacks to finish.
> 
> E.g. the following simple sequence on stack causes nasty crash:
> 
>     struct percpu_ref ref;
> 
>     percpu_ref_init(&ref, release, 0, GFP_KERNEL);
>     percpu_ref_kill(&ref);
>     percpu_ref_exit(&ref);

Hmmm... that's just an illegal sequence of operations.  You can't exit
a ref which hasn't completed killing yet (the kill callback hasn't
been called).

Thanks.

-- 
tejun